Fixing Sour Soil

Some plants thrive in sour soil.

Old-time gardeners referred to soil as either sweet or sour and knew which plants preferred which type of soil. Sour soil is classified as acidic and may even have a sour smell when tilled. Researchers discovered that the pH levels in the soil dictate whether the soil is acidic (sour), alkaline (sweet) or neutral.

Sour Soil Explained

If you compare your soil to a glass of milk, you gain a good perspective of what your plants go through. For instance, if you add vinegar to the milk it coagulates and can become sour cream. The sour cream has its uses. However, the milk is more rich, sweeter and has more uses if you add heavy cream. Most vegetables and flowers prefer the rich, sweet soil. You need to fix the sour soil to create a healthy growing medium for the plants.

pH Levels

The pH test kits measure the amount of hydrogen ions in the the soil. The soil becomes more acidic as the hydrogen ions increase. The test levels range from 0 to 14 with 7 being the neutral number. Test results below 7 indicate an acidic or sour soil and those above 7 indicate an alkaline or sweet soil. You can change the soil pH through the application of lime or sulfur. It is best to amend the soil about three months prior to planting.

Soil Additives

Sulfur lowers the pH level of the soil and will make it more sour. To sweeten the soured soil you must add lime. Lime comes in a variety of forms. It is available in powder form from many garden centers. Crushed oyster shells and wood ash also add lime to the soil. There are liquid applications available from nurseries and agriculture feed stores. The amount of lime needed to sweeten the soil depends upon the desired pH level. The amount of lime is generally listed as a percentage on the package and is calculated by pounds per acre or per 1,000 square feet. For instance, it takes about 60 pounds of lime for 1,000 square feet of sandy soil to increase the pH level. More lime is needed for loamy soils that are used for growing mushrooms or other plants that need a high pH.

Keeping Soil Sweet

The pH level changes may be slow and additives such as acidic peat moss can slow the process even further. Avoid acid-based fertilizers or chemicals so the pH level is not affected. Group acid-loving plants, such as blueberry bushes or azaleas, together so the fertilizers used for production do not interfere with the lime additives in the rest of the landscape.